The present invention relates to rotary regenerative air preheaters.
More particularly, the invention relates to the combustion air and flue gas inlets and outlets.
A rotary regenerative air preheater transfers sensible heat from the flue gas leaving a boiler to the entering combustion air through regenerative heat transfer surface in a rotor which turns continuously through the gas and air streams. The air preheater has a circular cross section to facilitate rotation of the rotor, which is packed with the heat transfer surface.
The air preheater is divided into a flue gas side or sector and one or more combustion air sides or sectors by sector plates. In a typical rotary regenerative heat exchanger, the hot flue gas and the combustion air enter the rotor shell from opposite ends and pass in opposite directions over the heat exchange material housed within the rotor. A duct system interconnecting the air preheater with the boiler includes a cool air duct for carrying cool combustion air to the air preheater, a hot air duct for carrying heated combustion air from the air preheater to the boiler, a hot flue gas duct for carrying hot flue gas from the boiler to the air preheater, and a cold flue gas duct for carrying cooled flue gas from the air preheater.
The duct work comprising the duct system generally has a rectangular cross section. Consequently, the combustion air inlet and outlet and the flue gas inlet and outlet includes apparatus to interface the rectangular ducts with the circular air preheater. The transition structure for such conventional inlets and outlets generally comprise multiple elements which are joined by numerous welds. Consequently, these transitions structures are time consuming and costly to construct. Further, conventional transition structures cannot be nested to reduce the overall volume for shipping, resulting in high shipping costs.
The present invention is a transition element for providing an interface between a duct having a substantially rectangular cross section and an air preheater having a substantially circular cross section. The transition element includes an inner sidewall, an outer sidewall, and first and second end walls, where the outer sidewall and the first and second end walls form first and second transition corners. Each of the transition corners comprises first and second flow deflectors, each having an outer terminal edge and first and second side edges extending laterally from the terminal edge to an inner point. The first side edge of the first flow deflector is mounted to the second side edge of the second flow deflector and the outer terminal edges of the first and second flow deflectors are mounted to the duct to connect the air preheater to the duct. Preferably, the first side edge of the first flow deflector is mounted to the second side edge of the second flow deflector by a weld seam.
Each flow deflector has a mid portion disposed intermediate the outer terminal edge and the inner point which is bowed toward the duct to provide the flow deflector with an arcuate shape. The arcuate shape of the flow deflectors and the weld seam connection between the flow deflectors provides a corner which is inherently stiffer than conventional corners.
The transition element also includes a duct mounting flange for mounting the transition element to the duct. The outer terminal edges of the first and second flow deflectors are mounted directly to the duct mounting flange by a second weld seam.
Depending on the application, the transition element may further include one or more stiffening elements mounted to the outside surface of one or more of the flow deflectors to provide additional mechanical strength.
An object of the invention is to provide a new and improved corner structure for the combustion air and flue gas inlets and outlets.
Another object of the invention is to provide a new and improved transition element for converting the rectangular structure of the duct work to the circular structure of the air preheater.
A further object of the invention is to provide a transition element which includes fewer components and is easier to manufacture and ship than conventional transition elements.